1. Field of the Invention
The present invention relates to a microcomputer, and more specifically, to a multi-channel serial interface circuit internally included in a microcomputer.
2. Description of Related Art
A serial interface function is internally provided in many microcomputers, since it can realize a data transfer with a small-number of terminals. In general, the serial interface has been such that data is transferred by using a serial data input terminal, a serial data output terminal and a clock terminal.
In recent application systems of microcomputers, it has become difficult for one microcomputer to perform all processings because of diversification in function of the application systems. Therefore, it is now more and more increasing that a main microcomputer is connected with a plurality of slave devices including a slave microcomputer and an electrically erasable ROM (read only memory) by means of a serial interface, so that the processing is shared so as to perform a whole control.
In the prior art, for example, if three channel interfaces are required in order to couple with three slave devices, a microcomputer has been constructed to internally include three channels of the same serial interface circuit blocks.
Thus, the structure of the conventional serial interface has given rise to an increase of a whole circuit scale of the microcomputer and a cost-up of the application system. In addition, since it is very difficult that the three channels of serial interface circuit blocks internally provided in the microcomputer ate simultaneously used by only one central processing unit provided in the microcomputer, it has been in many practical cases that only two channels are simultaneously operated, and the remaining only channel is utilized in an idle time. Therefore, the hardware resources internally provided in the microcomputer are not effectively utilized.